In the art, several processes are known for the preparation of solid catalytic components, suitable to be used in the polymerization of ethylene, and of its mixtures with alpha-olefins, comprising, as their essential components, halogenated compounds of magnesium, titanium, and an electron-donor compound. The polymers obtained by means of such catalysts are generally in powder form, with a more or less wide distribution of particle dimensions.
The use of such catalysts finds a certain limitation from the view point of the separation and of the carriage of the polymers, of the conditions of suspension polymerization, of stabilization, or of recovery of the polymer in the gas-phase polymerization processes.
The need is thus largely felt of having available catalysts endowed with a high activity, which allow polymers to be obtained in the form of particles having a narrow granulometric distribution, and furthermore endowed with a high bulk density.
Various methods have been proposed in the art for preparing such catalysts. One of them is disclosed, e.g., in European patent application No. 79102780.8, in the same Applicant's name, and consists in reacting a compound of Ti with a support consisting of, or comprising, an anhydrous Mg halide, in the form of spherical particles having an average diameter of 1-100 microns, a surface area greater than 500 m.sup.2 /g, and a porosity higher than 0.5 cm.sup.3 /g, and possibly also with an electron-donor compounds. A solid catalytic component is thus obtained which, when used with Al-or=ganometallic compounds, yields polymers in the form of particles having a narrow granulometric distribution, and endowed with high free-flowing properties. But in that case the technology is rather complex.
Another method is disclosed in European patent application No 83074 in the same Applicant's name, and consists in preparing an emulsion, in a silicone oil or in a hydrocarbon, of an immiscible liquid comprising a complex of MgCl.sub.2 with AlCl.sub.3 and with toluene and in reacting such an emulsion with Al-trialkyl, to precipitate a solid catalytic component. The catalysts obtained from such catalytic components yield polymers in the form of particles with a narrow granulometric distribution, but with a not yet satisfactory bulk density.